The present invention relates to sequence controllers in general and in particular to a sequence controller which produces a set of periodic control signals each having programmably determined frequency, relative phase relationship, duty cycle and periods of operation.
Many electronic circuits are controlled by complex patterns of high frequency clock signals which must have precisely controlled frequencies, phase relationships, duty cycles and periods of operation, but circuits needed to produce such clock signals are typically complex and expensive. Sequence controllers utilizing discrete logic can produce high frequency clock signals but typically cannot be easily modified in order to change the clock signal patterns produced. Programmable sequence controllers comprising high speed random access memories (RAMs) have been used in the past. When, for example, a RAM storing 8-bit data words is sequentially addressed while in a read mode, each output bit forms a separate clock signal which may oscillate according to the pattern of corresponding bits stored in the RAM, and each of the eight clock signals thus produced may have a different frequency, phase relationship and duty cycle. However, sequence controllers utilizing high speed RAMs are expensive and difficult to program and are often impractical when large numbers of clock signals having different periods, phase relationships, duty cycles and periods of operation are required.